Traditional aircraft taxi systems utilize the primary thrust engines (running at idle) and the braking system of the aircraft to regulate the speed of the aircraft during taxi. Such use of the primary thrust engines, however, is inefficient and wastes fuel. For this reason, electric taxi systems (i.e., traction drive systems that employ electric motors) have been developed for use with aircraft. Electric taxi systems are more efficient than traditional engine-based taxi systems because they can be powered by an auxiliary power unit (APU) of the aircraft rather than the primary thrust engines.
In its simplest form, a crew member may manually steer the aircraft during an electric taxi maneuver using a flight deck controller (e.g. a tiller) while looking out a window. In this case, the crew member utilizes their best judgment regarding execution of their taxi maneuver. An improvement over this process is provided by a visual guidance system wherein a crew member enters airport parameters such as airport congestion, the visual guidance system determines the best taxi path, subject to ATC clearance, and presents it on a cockpit display along with instructions as to the best way to navigate the aircraft along the suggested taxi path; e.g. speed, steering, when to thrust engines off and turn electric drive motors on, etc. ATC clearance can include taxi route, assigned take-off or landing runway, hold points etc. and is considered in the calculated path.
While effective, the above described visual guidance system exhibits certain inefficiencies. For example, variations in complying with display guidance instructions, even in the neighborhood of a few seconds, may decrease fuel savings; e.g. a pilot waits a short time before turning thrust engines off. The pilot may execute faster turns than necessary resulting in increased tire wear, or brake more often than necessary causing unnecessary wear and tear on the braking system. In addition, some actions that would increase efficiency are too subtle for the crew to recognize and manage; e.g. optimum acceleration of the aircraft during taxi.
Accordingly, it would be desirable to provide an electric taxi automatic guidance and control system, capable of guiding and controlling an aircraft during a taxi maneuver with minimal crew intervention thus increasing efficiency and reducing the work load of the crew.